Methanogenesis is the main route of hydrogen (H2) disposal during the process of rumen fermentation (Beauchemin et al., 2008). Removal of H2 from the rumen milieu is essential for the efficient continuation of rumen fermentation, but the methane resulting from methanogenesis has been implicated both as a loss of dietary energy to the animal (Johnson and Johnson, 1995) as well as a significant greenhouse gas contributing to global warming (Steinfeld et al., 2006). Both subjects have led to a global search for feed additives to mitigate methane production from ruminants.
One of the options explored to reduce methane emissions is the redirection of excess H2 into processes that yield more beneficial products for the ruminant, thereby lowering methanogenesis. Examples include the stimulation of propiogenesis by addition of propionate precursors and attempts to introduce reductive acetogenesis into the rumen (Joblin, 1999, Molano et al., 2008). Successful induction of these processes in the rumen would respectively yield propionate or acetate as nutrients for the animal, while at the same time reducing the availability of H2 for methanogenesis. However, the introduction of propionate precursors (malate and fumarate) has yielded variable effects on methane production (Asanuma et al., 1999, Ungerfeld et al., 2007) and attempts to introduce reductive acetogenesis in the rumen have failed so far because of a lower affinity for hydrogen when compared to methanogenesis (Le Van et al., 1998).
Another options for reducing methane emissions has been described in U.S. Pat. No. 5,843,498, which concerns ruminant feed compositions for depressing rumen methanogenesis and improving feed efficiency comprising, as an effective component, cysteine and/or its salts.
A small number of research groups have looked into the potential of nitrate as methane reducing feed additive, and the addition of nitrate appears to consistently lower methanogenesis (Guo et al., 2009, Sar et al., 2005, Takahashi et al., 1998).
The possibility to introduce nitrate (NO3) as alternative hydrogen sink to reduce methanogenesis in the rumen has been largely ignored, due to consistent findings of toxic effects from nitrite that is formed as an intermediate during the reduction of nitrate to ammonia in the rumen (Lewis, 1951). High doses of nitrate in ruminant diets have been reported to cause methemoglobinemia, reducing the blood's capacity to transport oxygen to the animals' tissues. In addition, nitrite accumulation in the rumen is known to reduce microbial activity in the rumen, which inter alia may reduce feed intake by the animal.
It has been suggested to supplement high nitrate fed ruminants with formate, lactate or fumarate, in order to alleviate the inhibitory effect of nitrite on fermentation (Iwamoto, 1999; Iwamoto, 2001). The simultaneous administration of nitrate and GOS or nisin has also been reported as an effective measure to lower the concentration of rumen and plasma nitrite and methemoglobin, while keeping rumen methanogenesis at a low level, as compared to nitrate treatment alone (Sar, 2004).
Acceleration of nitrite reduction using probiotics has also been the subject of extensive research. U.S. Pat. No. 6,120,810 teaches to decrease ruminant intoxication by nitrates by administering to the animal a composition containing an effective amount of the nitrite reducing microorganism Propionibacterium acidiproprionici. European patent application no. 1 630 226 discloses a feed composition for ruminants containing a microbe having nitrite reductase activity, which is selected from intestinal bacteria, coryneform bacteria, Bacillus subtilis, bacteria of the genus Methylophilus, Actinomyces, ruminal bacteria and combinations thereof. It has also been reported (Sar, 2005) that E. Coli W3110 might be used to abate intoxication when nitrate is used to inhibit methanogenesis in ruminants.
Inhibitory effects of sulphur compounds, copper and tungsten on nitrate reduction have been investigated (Takahashi, 1989). The authors report that in rumen fluid from nitrate adapted wethers (0.55 g NaNO3/kg body weight twice daily) nitrite formation was affected neither by incubation with Sulphate-S nor by incubation with sulphite-S. Of the S-containing amino acids, methionine proved to be inefficient in inhibiting microbial reduction of nitrate whereas cystein significantly lowered nitrite formation. This publication did not concern or address any methanogenesis reducing effects. The effectiveness of cystein in preventing nitrite accumulation was confirmed in later studies (Takahashi, 1991; Takahashi 1998).
It is the primary objective of the present invention to provide treatments, and the compositions for use therein to further reduce methanogenesis in ruminants while avoiding or overcoming the particular problems associated with nitrite accumulation.